Pressure relief valves are well known in containers under pressure, such as for example silos, which are provided with a metal discharge duct, which can be connected to a further pipe for conveying powders to a confined and protected area.
Even tough these valves work in an excellent manner, they present the drawback that, in the long run, the powder that has been discharged can partly settle on the curve of the discharge and/or on the closing membrane of the discharge itself, thus requiring periodic cleaning and maintenance.
Possible solutions based on the use of rigid plastic materials instead of metal materials could probably lead to lower costs of the plant, but they would also cause significant wear problems as well as problems linked to the scaling of the discharge duct of the valve.
As of today, no solution to this problem has been found, except for the aforementioned solution, which requires anyway a periodic maintenance of the vale.
The solution according to the present invention provides an industrialized valve body made of plastic material, which comprises, though, a powder discharge duct made of a flexible material, for example an elastomer, in particular a polymer that is suited to be elastically deformed.
The powder discharge duct is constrained at its ends, so that the increase in pressure, due to the loading of the silo, causes it to be squashed and deformed, while, during the opening of the discharge, it resumes its original shape. This original shape squashing/resuming movement allows the powder discharge duct to vibrate, thus eliminating possible scaling.
During the discharge phase of the emission part of the dusty material is deposited on the exhaust pipe and stays there until the next rise of the internal pressure of the silo.
The pulsed action which acts on the exhaust pipe, before the opening of the valve according to the invention, allows the almost total removal of the material present and the detachment from the walls of those that might be encrusted. The activation of the deformation takes place already at pressures lower than those of the standard settings normally adopted by the normal pressure control valves (+500 mmH2O). The subsequent flow of material and air, with regard to the ratio of such a flow, will clean completely the duct thereby preventing the obstruction of the same. All this to guarantee the safety of operation and function of the valve itself, with a remarkable increase in the safety of people and the plant.
Even though there can be embodiments having straight and inclined pipes, one of the preferred embodiments of the present invention is based on the use of a curved discharge duct having a thickness ranging from 3 mm and 12 mm.